This invention relates to a data acquisition system in a hot metal handling operation, and in particular, to a system for use with electrolytic aluminium reduction pots.
In the past, the aluminium smelting industry operated their plants almost entirely manually and the operation was more an art than a science and plant efficiency depended mainly on the skill and experience of the operating personnel.
During the last two decades or so, various efforts have been made to make a transition from art toward science in the control of pot operation. The main problem has been the complete lack of suitable control systems, and the lack of knowledge to develop complex controls.
During the last ten years, predominantly electrical resistance control of pot operation has been introduced almost throughout the aluminium industry. This system requires the simultaneous measurement of individual pot potentials and line current. These parameters have been used to compute the individual pot resistances and compare them to an assigned target and to raise or lower the anodes automatically, so as to keep the pot resistances at an individual predetermined value.
Almost all such systems employ a computer to operate on acquired data to effect associated control functions. The computer, however, is used as a blind executive element or a simple calculating machine without any judgment, and it will follow the target pot resistance set by the operator, whether or not that is the resistance at which the pot operates most efficiently.
Essential information was missing to enable the decision-making ability of the computer to control the individual pots and to obtain highest efficiency in lines which, it should be noted, comprise two rows of pots each containing up to about 240 series-connected pots in individual pot rooms that can be as long as 4000 feet.
It was recognized that these pots frequently operate below normal efficiencies for prolonged periods of time.
It is obvious that if the individual performance of the pots can be monitored by the computer, the operation of the inefficient pots can be adjusted in proper time and, if adequate information is at hand, the necessary programs can be provided to restore them to high operating efficiency.
It has been recognized that previous technology for controlling smelters did not provide a sufficiently broad spectrum of information to achieve such individual efficiency control.
Such control entails the accurate measurement of certain pot parameters such as the inflow and outflow of materials; heat conditions; changes in electrolyte freeze contour configurations; variations in cathode resistance; and rate of specific carbon consumption. It is also required that instructions are generated, transmitted and effected so as to maintain each individual pot as close to optimum operation as possible through, for instance, timely additions of alumina to the electrolyte, timely removal of the optimum amount of metal and appropriate positioning of the anode of each pot with respect to the cathode.
It would be impractical to feed the computer with information about such parameters by a conventional system using wire connections since the cost would be prohibitive and its maintenance very difficult.
In each pot room there usually exists an overhead crane moving on rails over the pots. This crane is used to service the pots.